As typical manufacturing techniques for an optical transmission body (for example, an optical fiber), there have been proposed: 1) a method of melting and drawing down a preform by an interface gel polymerization method; 2) a screw extrusion method; and 3) an extrusion method using a gas pressure (Patent Document 1).
For optical use and for use as the optical fiber, optical polymer/fiber excellent in transparency and optical transmittance are required. With regard to this optical transmittance, quality performance thereof is deteriorated by impurities/foreign objects contained in a polymer constituting the fiber. For example, the impurities mentioned herein include those caused by oxidation degradation of the polymer due to oxygen contained in air or an extrusion system, thermal degradation of the polymer due to heat given thereto beyond a pot life, and the like. Moreover, as the foreign objects, there are typically mentioned: organic matter such as fiber adhered to a surface of a supplied material; inorganic matter such as dust; human skin coming from a worker; and the like.